[5.6] Fix a unsuspected result from the split function in the Collection class

[tvbeek]

See: #22090

This will change the result of the split function to return the requested amount of collections (except the total of items is less then the requested number)

Example
collect(['a', 'b', 'c', 'd'])->split(3);

// expected and new result
[['a', 'b'], ['c'], ['d']]

// result before this change
[['a', 'b'], ['c', 'd']]

It will change the split function and add 3 new tests to test some edge cases that are fixed with this change

[taylorotwell]

Not going to change this on a point release.

[tvbeek]

@taylorotwell Will you accept it on the master branch?